1. Field of the Invention
The present invention is for an intracorneal lens, and more particularly, pertains to a small intracorneal lens with two regions of focality.
2. Description of the Prior Art
Three prior art patents, Choyce (U.S. Pat. No. 4,607,617), Grendahl (U.S. Pat. No. 4,624,669) and Lindstrom (U.S. Pat. No. 4,851,003), for intracorneal lenses describe large lenses or do not teach a bifocal or multifocal effect.
Barrett et al. (U.S. Pat. No. 5,196,026) describe a small intracorneal lens that does not significantly impede nutrient flow through the cornea and only involves a small optical region of the cornea. The region of cornea that surrounds the perimeter of the device of Barrett et al. is not optically affected by their lens. Barrett disclose a "bull's-eye" intracorneal lens that contains a hole drilled out of the center of the lens which will allow flow of nutrients through the cornea. One does not know from the Barrett et al. description if the aperture made in the lens should be a pin hole or if it should be large in comparison to the optical zone of the cornea. Barrett et al. teach a smaller lens that does not require an aperture and does not impede nutrient flow due to its small diameter size.
Shepard (U.S. Pat. No. 4,994,080) discloses a lens that has an aperture in it, but it is not suitable for an intracorneal inlay. Shepard describes an optical lens that has application for a contact lens, a corneal overlay, or as an artificial implanted lens replacement. The lens has at least one, but can contain several, small pin holes, which are referred to as stenopaeic openings. These openings are intended to pass only those light beams that are parallel to the central axis of the stenopaeic opening back onto the retinal portion of the eye. This method of light focusing through pin holes can be very limiting in terms of field of view and limits the size of image that can be adequately focused. It is furthermore doubtful that such a lens would have any application as an intracorneal inlay due to the anticipated growth of corneal stromal tissue into the pin hole of Shepard's device, thereby limiting its usefulness as an intracorneal lens.
The present intracorneal inlay device is designed to overcome the limitations of prior art devices and provide for multifocality.
The present invention overcomes the disadvantages of the prior art by providing a small intracorneal lens where the intracorneal lens provides two focal regions of specific configuration. The central region provides adequate area for imaging at one focal length, and the surrounding area provides imaging at a second focal length. The transition is designed to minimize distortion of the image.